<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>显示当前系统时间</button>
    <div>某个时间</div>
    <script>
        1.//获取元素
        var btn = document.querySelector('button');
        var div = document.querySelector('div');
        //2.注册事件
        btn.onclick = function(){
            div.innerText = '2019-6-6';
            
        }
    </script>
</body>
</html>